In the foundry industry, one of the procedures used for making metal parts is by sand casting. In sand casting, disposable molds and cores are fabricated with a mixture of sand and an organic or inorganic binder. The binder is usually used to strengthen the cores, which are the most fragile part of the mold assembly.
One of the fabrication processes used in sand casting is the cold-box process. In this process a gaseous curing agent is passed through a mixture of the sand and binder to cure the mixture. Another fabrication process used in sand casting is the no-bake process which employs a liquid curing catalyst. In general, the cold-box process is used for making cores and smaller castings while the no-bake process is used for making molds and larger castings.
Binders commonly used in the cold-box and no-bake fabrication processes are polyurethane binders derived from curing a polyurethane-forming binder composition with a tertiary amine catalyst. The polyurethane-forming binder composition usually consists of a phenolic resin component and polyisocyanate hardener component. Such polyurethane-forming binder compositions, used in the cold-box process and no-bake process, have proven satisfactory for casting such metals as iron or steel which are normally cast at temperatures exceeding about 2500 degrees Fahrenheit. They are also useful in the casting of light-weight metals, such as aluminum, which have melting points of less than 1500 degrees Fahrenheit.